Bright field-dark field illumination system

ABSTRACT

An illumination system for bright field/dark field microscopy has a swinging deflector which is normally positioned on the optical axis when bright field microscopy is used and which is swung off the optical axis when dark field microscopy is used. When the deflector is swung off the optical axis an alternate illumination axis is utilized to provide a reduced portion of the observation axis having coaxial counterflowing light passing there along.

BACKGROUND OF THE INVENTION

The present invention relates to microscope illuminators and moreparticularly to microscope illuminators for bright field/dark fieldmicroscopy with an alternate light passage for dark field microscopy.

Prior Art

U.S. Pat. No. 1,943,510 was issued Jan. 16, 1934 to Bauersfeld et al anddiscloses a vertical illumination system in FIG. 2 which may be used foreither bright field or dark field microscopy. The vertical illuminationsystem uses an annular mirror 12 and an occluder 19-19' to permit eitherbright field or dark field microscopy. The same illumination axis isused for both bright field and dark field microscopy although differentportions of the path are utilized for the different types of microscopy.

U.S. Pat. No. 1,840,448 issued to Heine Jan. 12, 1932 illustrates a darkfield illuminator having a beam splitter or annular reflector to directlight toward the object.

U.S. Pat. No. 2,079,621 was issued May 11, 1937 to Land and discloses anannular ring reflector used in a vertical dark field microscopeilluminator.

U.S. Pat. No. 2,097,762 issued Nov. 2, 1937 to Heine and discloses anannular ring used in a vertical dark field microscope illuminator.

U.S. Pat. No. 3,752,560 issued Aug. 14, 1973 to Lunn and discloses anincident light dark field illumination system having an annularreflector with a semi-transmissive/semi-reflective central portion thatmay be used for bright field vertical illumination when lens 7 isremoved from the optical path. The system has the same illumination axisfor both dark field and bright field microscopy.

BRIEF DESCRIPTION OF THE PRESENT INVENTION AND DRAWING

The bright field/dark field illuminator of the present invention has analternate illumination axis for dark field microscopy. By removing aconventional partially transmissive mirror used for vertical brightfield illumination, light from the illuminator enters the alternateillumination axis and is reflected by an annular surface onto theobject. The alternate axis provides a shorter co-axialillumination/observation path for dark field microscopy to reduce noisecaused by adjacent light rays traveling in opposite directions.

FIG. 1 is an optical diagram of the illuminator showing its location inan incident microscope system and

FIG. 2 is an enlargement of the portion of the illumination systemshowing the movable mirror.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

Referring to FIG. 1, light from the filament is collected by lenses Iand II, modified by lens III and, after passing through the aperturediaphragm and field diaphragm, the filament image is focused by doubleIV, near the shoulder ofthe objective for bright field microscopy.Semi-transmissive mirror 1, is located between the microscope objectiveand eyepiece to deflect light from lens IV along the observation axistoward the objective. Although the objective of an infinity-correctedmicroscope moves for focusing which changes the relative position of thefilament image with respect to the objective shoulder, the location ofthe filament image is not critical for bright field microscopy.

Referring to FIG. 2 microscope body 1 has lens holder 2 positionedtherein to position lens IV. Support 3 extends from lens holder 2 andhas mirror mount 4 pivotably connected thereto. Arm 5 from mirror mount4 extends through opening 6 in microscope body 1. When desiring topractice dark field microscopy, the observer swings mirror 1 off theobservation axis by shifting arm 5 to the position shown in dottedoutline.

Referring again to FIG. 1, light passes along the alternate illuminationaxis represented by spacings 9, 10, 11, 12 and 13, when mirror M₁ isswung off the observation axis. Lens V collimates light received fromlens IV and mirror M₂ deflects the light along a path parallel toobservation axis. Positive lens VI receives the collimated light frommirror M₂ which is then deflected by mirror M₃ and the reflectiveannulus near the objective shoulder. In infinity-corrected microscopes,the nosepiece containing the objective moves for focusing. By providinga collimated zone between mirror M₂ and lens VI, the position of theimage reflected by the reflective annulus maintains the same relativeposition with respect to the objective shoulder. This position criticalfor dark field microscopy.

The parameters of the illumination system are set forth in the Tablebelow. The Table is divided into two sections, with bright filedparameters being on the left and dark field parameters being on theright. Lens radii are designated R₁ -R₁₃, wherein a minus sign (-)applies to a surface whose center of curvature lies away from thefilament side of its respective vertex. Successive axial spacings aredesignated S₁ -S₁₅ and lens thicknesses are designated T₁ -T₇. Radii,thicknesses and axial spacings are all in millimeters. The indices ofrefraction and Abbe numbers of the glasses are designated ND₁ -ND₇ andν₁ -ν₇, respectively.

                                      TABLE                                       __________________________________________________________________________    BRIGHT FIELD                                                                                             Index of                                                                             Abbe                                           Radius  Thickness                                                                           Spacing   Refraction                                                                           No.                                         Lens                                                                             (R)     (T)   (S)       (ND)   (ν)                                      __________________________________________________________________________                     S.sub.1 = 8.00                                                  R.sub.1 = 89.448                                                           I          T.sub.1 = 4.5   ND.sub.1 = 1.523                                                                     ν.sub.1 = 58.6                              R.sub.2 = -9.269                                                                            S.sub.2 = 0.10                                                  R.sub.3 = 40.643                                                           II         T.sub.2 = 5.0   ND.sub.2 = 1.523                                                                     ν.sub.2 = 58.6                              R.sub.4 = -16.726*                                                                          S.sub.3 = 65.06                                                 R.sub.5 = 30.280                                                           III        T.sub.3 = 4.0   ND.sub.3 = 1.523                                                                     ν.sub.3 = 58.6                              R.sub.6 = -30.280                                                                           S.sub.4 = 4.00                                                                S.sub.5 = 54.00                                                               S.sub.6 = 44.01                                                 R.sub.7 = 52.780                                                           IV         T.sub. 4 = 2.5  ND.sub.4 = 1.785                                                                     ν.sub.4 = 25.7                              R.sub.8 = 22.736                                                                      T.sub.5 = 7.0   ND.sub.5 = 1.548                                                                     ν.sub.5 = 45.8                              R.sub.9 = -33.268                                                                           S.sub.7 = 12.00                                                               S.sub.8 = 61.00 to 75.50                                                      S.sub.14 = 18.00                                                              S.sub.15 = 1.64                                              __________________________________________________________________________    DARK FIELD                                                                                               Index of                                                                             Abbe                                           Radius  Thickness                                                                           Spacing   Refraction                                                                           No.                                         Lens                                                                             (R)     (T)   (S)       (ND)   (ν)                                      __________________________________________________________________________                     S.sub.1 = 8.00                                                  R.sub.1 = 89.448                                                           I          T.sub.1 = 4.5   ND.sub.1 = 1.523                                                                     ν.sub.1 = 58.6                              R.sub.2 = -9.269                                                                            S.sub.2 = 0.10                                                  R.sub.3 = 40.643                                                           II         T.sub.3 = 5.0   ND.sub.2 = 1.523                                                                     ν.sub.2 = 58.6                              R.sub.4 = -16.726*                                                                          S.sub.3 = 65.06                                                 R.sub.6 = 30.280                                                           III        T.sub.3 = 4.0   ND.sub.3 = 1.523                                                                     ν.sub.3 = 58.6                              R.sub.6 = -30.280                                                                           S.sub.4 = 4.00                                                                S.sub.5 = 54.00                                                               S.sub.6 = 44.01                                                 R.sub.7 = 52.780                                                           IV         T.sub.4 = 2.50  ND.sub.4 = 1.784                                                                     ν.sub.4 = 25.7                              R.sub.8 = 22.736                                                                      T.sub.5 = 7.0   ND.sub.5 = 1.548                                                                     ν.sub.5 = 45.8                              R.sub.9 = -33.268                                                                           S.sub.7 = 12.00                                                               S.sub.9 = 41.60                                                 R.sub.10 = -19.580                                                         V          T.sub.6  = 2.50 ND.sub.6 = 1.523                                                                     ν.sub.5 = 58.6                              R.sub.11 = ∞                                                                          S.sub.10 = 9.90                                                               S.sub.11 = 40.88 to 55.38                                       R.sub.12 = 115.723                                                                    T.sub.7 = 4.5   ND.sub.7 = 1.648                                                                     ν.sub.7 = 33.9                              R.sub.13 = 115.723                                                                          S.sub.12 = 15.62                                                              S.sub.13 = 51.50                                                              S.sub.14 = 18.00                                                              S.sub.15 = 1.64                                              __________________________________________________________________________     *aspheric surface                                                        

The surface of singlet II with radius R₄, is an axially symmetricalaspheric surface with Z axis of revolution. The value of Z for any givenvalue of x and y, is defined by the equation: ##EQU1## whereind=1.0181×10⁻⁴

e=-3.4136×10⁻⁷

f=3.107×10⁻⁸

g=-2.9372×10⁻⁹

p² =x² +y²

c=1R₄ and

k=-1.0

The mathematical support for this formula and explanation may be foundin the Military Standard Handbook, MIL-HBDK-141 (50CT62), Sec. 5.5.1,Page 5-13 to 5-21.

What is claimed is:
 1. A vertical bright-field and dark-field microscopeilluminator having a light source and a microscope objective with ashoulder aligned on an optical axis, which comprises, a first lenssystem for collecting light from the source, a second lens system forreceiving light from said first lens system and focusing an image of thesource, a partially transmissive mirror selectively positionable on theoptical axis to deflect light from said second lens system toward theobjective for bright-field microscopy, an annular reflector located onthe optical axis near the objective, an alternate optical axis used whensaid mirror is positioned off the optical axis, a relay system on saidalternate optical axis to focus light presented to said annularreflector near the objective shoulder for dark-field microscopy.
 2. Thevertical bright-field and dark-field microscope illuminator of claim 1wherein the relay system has a zone of collimated light to maintain aconstant relationship between the image and the objective shoulderduring dark-field microscopy.
 3. The vertical bright-field anddark-field microscope illuminator of claim 1 wherein said first lenssystem includes a biconvex positive singlet I and a biconvex singlet IIwith an axially-symmetrical, aspheric second surface, said second lenssystem includes a biconvex positive singlet III and a biconvex positivedoublet IV and said relay system includes a concave-plano negativesinglet V, a mirror M₂, biconvex positive singlet VI and a Mirror M₃. 4.The vertical bright-field and dark-field microscope illuminator of claim3 having the parameters set forth below wherein successive lens radiiare designated R₁ -R₁₅, where a minus sign indicates a radius of centerof curvature lying opposite the source filament side of its vertex,axial thicknesses of successive lens elements are designated T₁ -T₇,successive axial spaces are designated S₁ -S₁₅, radii, thickness andspacings all being in millimeters, refractive indicies and Abbe numbersof the successive lens elements are designated ND₁ -ND₇ and ν₁ -ν₇,respectively;

    __________________________________________________________________________    BRIGHT FIELD                                                                                             Index of                                                                             Abbe                                           Radius  Thickness                                                                           Spacing   Refraction                                                                           No.                                         Lens                                                                             (R)     (T)   (S)       (ND)   (ν)                                      __________________________________________________________________________                     S.sub.1 = 8.00                                                  R.sub.1 = 89.448                                                           I          T.sub.1 = 4.5   ND.sub.1 = 1.523                                                                     ν.sub.1 = 58.6                              R.sub.2 = -9.269                                                                            S.sub.2 = 0.10                                                  R.sub.3 = 40.643                                                           II         T.sub.2 = 5.0   ND.sub.2 = 1.523                                                                     ν.sub.2 = 58.6                              R.sub.4 = -16.726*                                                                          S.sub.3 = 65.06                                                 R.sub.5 = 30.280                                                           III        T.sub.3 = 4.0   ND.sub.3 = 1.523                                                                     ν.sub.3 = 58.6                              R.sub.6 = -30.280                                                                           S.sub.4 = 4.00                                                                S.sub.5 = 54.00                                                               S.sub.6 = 44.01                                                 R.sub. 7 = 52.780                                                          IV         T.sub.4 = 2.5   ND.sub.4 = 1.785                                                                     ν.sub.4 = 25.7                              R.sub.8 = 22.736                                                                      T.sub.5 = 7.0   ND.sub.5 = 1.548                                                                     ν.sub.5 = 45.8                              R.sub.9 = -33.268                                                                           S.sub.7 = 12.00                                                               S.sub.8 = 61.00 to 75.50                                                      S.sub.14 = 18.00                                                              S.sub.15 = 1.64                                              __________________________________________________________________________    DARK FIELD                                                                                               Index of                                                                             Abbe                                           Radius  Thickness                                                                           Spacing   Refraction                                                                           No.                                         Lens                                                                             (R)     (T)   (S)       (ND)   (ν)                                      __________________________________________________________________________                     S.sub.1 = 8.00                                                  R.sub.1 = 89.448                                                           I          T.sub.1 = 4.5   ND.sub.1 = 1.523                                                                     ν.sub.1 = 58.6                              R.sub.2 = -9.269                                                                            S.sub.2 = 0.10                                                  R.sub.3 = 40.643                                                           II         T.sub.3 = 5.0   ND.sub.2 = 1.523                                                                     ν.sub.2 = 58.6                              R.sub.4 = -16.726*                                                                          S.sub.3 = 65.06                                                 R.sub.6 = 30.280                                                           III        T.sub.3 = 4.0   ND.sub.3 = 1.523                                                                     ν.sub.3 = 58.6                              R.sub.6 = -30.280                                                                           S.sub.4 = 4.00                                                                S.sub.5 = 54.00                                                               S.sub.6 = 44.01                                                 R.sub.7 = 52.780                                                           IV         T.sub.4 = 2.50  ND.sub.4 = 1.784                                                                     ν.sub.4 = 25.7                              R.sub.8 = 22.736                                                                      T.sub.5 = 7.0   ND.sub.5 = 1.548                                                                     ν.sub.5 = 45.8                              R.sub.9 = -33.268                                                                           S.sub.7 = 12.00                                                               S.sub.9 = 41.60                                                 R.sub.10 = -19.580                                                         V          T.sub.6 =  2.50 ND.sub.6 = 1.523                                                                     ν.sub.5 = 58.6                              R.sub.11 = ∞                                                                          S.sub.10 = 9.90                                                               S.sub.11 = 40.88 to 55.38                                       R.sub.12 = 115.723                                                                    T.sub.7 = 4.5   ND.sub.7 = 1.648                                                                     ν.sub.7 = 33.9                              R.sub.13 = 115.723                                                                          S.sub.12 = 15.62                                                              S.sub.13 = 51.50                                                              S.sub.14 = 18.00                                                              S.sub.15 = 1.64                                              __________________________________________________________________________     *aspheric surface                                                        